BOSTON — Lawyers for former state Probation Commissioner John O'Brien want the federal judge presiding over his trial to bar witnesses from using the words "rigged" or "sham."

In a series of motions filed Monday, O'Brien's lawyers said the words in question "are not based on personal observation and are inadmissible opinion testimony that usurps the jury's role" in deciding the issue.

O'Brien and two deputies face racketeering charges. Prosecutors say they oversaw a hiring system in which candidates recommended by lawmakers were hired over more qualified candidates in exchange for favorable treatment come budget time.

They have pleaded not guilty.

The Boston Globe reports that prosecutors wrote that O'Brien is being charged with the very concept the defense wants to keep jurors from hearing about.